It's usually best to PRIME/SEAL. However, a pro can best determine if he can get away with not doing it. For example, if you're changing from a light-colored wall now to a dark one, you MAY not have to paint. It depends how light and how dark. See what I mean?
So I agree - PRIME/SEAL to be sure. One coat of P/S is fine. In short, I'd go w/2 coats of finish paint. (Not that many folks are THAT good that they can get away w/just one coat. Me included!)
My best to ya and hope this helps.
Jay J -Moderator
Primer is used either on a new, unpainted surface or on an old, dirty surface.
Its purpose is twofold. First, it seals the surface. Primer does not soak in like regular paint. Regular paint on rough-grade wood just soaks in like the wood is a sponge, and it soaks so deep that the next few coats will continue to soak in. You can paint five coats before the paint really stops seeping in. Same thing with new drywall/joint compound, although not as pronounced. Primer provides a sealer coat that makes the surface better for regular paint.
Second, primer adheres better to unpainted surfaces than regular paint, thus making it less likely the paint will chip or peel off. That is why you should use it on old painted surfaces: because the adhesion would not be good anymore on the old, dirty surface. So, again, two coats of paint is NOT the same as one coat primer, one coat paint.
If you have a recently painted surface (past five to ten years), do not bother with primer unless the surface is dirty (say, in a kitchen exposed to greasy smoke).
[This message has been edited by Lawrence (edited July 14, 2001).]